I am about to buy a 2002 JGC Overland. I notice that the vehicle says "premium fuel RECOMMENDED." To me, recommended and required are 2 different things. Do you know if running regular gas will harm the engine or will the performance just be hindered? All I know is that the H.O. engine has a higher compression ratio, but it does not have an advance spark timing like the 5.9 did, and that one required premium. Thanks.